Update README

README.md

@@ -1,10 +1,12 @@
-# Tres - a Elixir OpenFlow development platform
+# Tres - an Elixir OpenFlow development platform
 
 ## Overview
 
 Tres is a framework and set of helper libraries to develop OpenFlow controllers in Elixir.
 
-## Installation
+## How to build your own controller application
+
+### Installation
 
 ```elixir
 def deps do
@@ -14,7 +16,7 @@ def deps do
 end
 ```
 
-## callbacks
+### callbacks
  
 ```elixir
 config :tres,
@@ -27,8 +29,49 @@ This module must implement the `Module.start_link/2` that returns `on_start`.
 
 Set the callback_args to the terms you want pass to the `start_link/2` callback function.
 
+```
+% cat lib/sample.ex
+defmodule Sample do
+  use GenServer
+  use Tres.Controller
+
+  def start_link(datapath_id, _start_args) do
+    GenServer.start_link(__MODULE__, [datapath_id])
+  end
+  
+  def init([datapath_id]) do
+    # As an example create a flow to receive all packet_ins from port 1
+    redirect_action = Output.new(:controller)
+    apply_ins = ApplyActions.new(redirect_action)
+    match = Match.new(in_port: 1)
+    :ok = send_flow_mod_add(datapath_id, 
+                            priority: 1,
+                            match: match,
+                            instructions: [apply_ins])
+    {:ok, datapath_id}
+  end
+  
+  def handle_info(%PacketIn{} = packet_in, datapath_id) do
+    # print the packet_in message struct
+    IO.inspect(packet_in)
+    {:noreply, datapath_id}
+  end
+end
+```
+
+## To run the controller
+
+```bash
+$ iex -S mix
+```
+
 ## Examples
 
 - learning-switch: Simple Layer2 switch
-- leader-example: Simple Leader election based multiple controller
+- leader-example: Simple election based multiple controller using Ulf Wiger's Locks Leader
 
+License
+-------
+Tres is released under the Apache license Version 2.0:
+
+* https://www.apache.org/licenses/LICENSE-2.0